1) Field of the Invention
The present invention relates to friction welding and, in particular, relates to an apparatus and method for using electromagnetic radiation to provide heat during friction welding.
2) Description of Related Art
Friction welding, as is known in the art, typically includes generating a frictional force between a tool and a workpiece comprising one or more structural members to form a plasticized region of the structural members, in which the materials of the structural member are plasticized, mixed, and thereafter cooled to form a friction weld joint. In one conventional method, the tool is a rotary tool such as a friction stir welding tool, which includes a rotatable shank and pin. The shank and pin are rotated, and the pin is urged into one of the structural members or into an interface between adjacent structural members. As the pin rotates, friction between the pin and the structural members heats the structural members and forms a plasticized region, in which the materials of the structural members become plastic but generally not melted. The rotational motion of the pin also mixes the materials of the structural members in the plasticized region. The pin is translated through the structural members or along the interface to form a linear friction stir weld joint. In another conventional method, the friction welding tool is reciprocated instead of rotated.
Friction welding can provide strong and reliable weld joints and can be used with a variety of materials, such as steel, titanium, aluminum, and alloys thereof, some of which are difficult to join by other welding methods such as arc welding. Thus, friction welding provides an alternative to other types of welding as well as fasteners, such as screws, bolts, rivets, and the like. The speed and, hence, the cost effectiveness of friction welding, however, is limited by the speed at which the tool is translated through the structural members. If the tool is translated too quickly, the frictional heat generated between the tool and the structural members will not be sufficient to plasticize the structural members, decreasing the quality of the resulting weld joint. Thus, the translational speed of the tool is generally limited by the rate at which frictional heat is generated between the tool and the structural members.
One proposed method of friction welding includes providing additional heat to the structural members to supplement the frictional heating achieved by the friction welding tool. For example, an electric current can be passed through the structural members, resulting in resistive heating in the structural members. Alternatively, induction heaters or lasers can be used to heat the structural members. However, the effective heating that results in the structural members can vary according to the characteristics of the individual structural members. For example, the resistance, inductance, and surface reflectance of the structural materials can affect the amount of heating that occurs from resistive heating, inductive heating, and laser heating, respectively. Additionally, the heating may not be limited to the immediate region of the weld joint but may affect a larger region of the structural members, sometimes referred to as a xe2x80x9cheat affected zone,xe2x80x9d which is characterized by adverse material properties, such as increased brittleness, caused by heating. A large heat affected zone caused by the additional heating reduces the quality of the weld joint and can require additional processing to restore the initial material properties.
Thus, there exists a need for a friction welding apparatus and method for forming strong and reliable friction weld joints in a variety of materials. The apparatus and method should provide heat to the structural members to supplement the frictional heat generated between the friction welding tool and the structural members and thereby increase the maximum welding speed. The apparatus and method should also provide consistent heating of different structural members and allow the heating to be limited to a particular area of the structural members.
The present invention provides an apparatus for friction welding at least one structural member. The apparatus includes a shank and a probe that is connected to the shank. The probe is configured to be actuated by the shank for friction welding the at least one structural member. At least one of the shank and probe defines an absorption surface and a cavity that extends thereto. The absorption surface is configured to receive electromagnetic radiation from an electromagnetic radiation source for heating the probe. The absorption surface can be internal and/or oblique to a direction of the electromagnetic radiation received from the electromagnetic radiation source. The absorption surface can also be curved and/or conical. According to one aspect of the invention, the probe defines at least one aperture extending through the absorption surface such that electromagnetic radiation can propagate from the cavity through the aperture and impinge on the structural member.
The apparatus can also include the electromagnetic radiation source, which is configured to irradiate the absorption surface and thereby heat the probe and the structural members. The electromagnetic radiation source can be a light source or a radio frequency generator, and a fiber optic cable or a waveguide can be provided for directing the radiation toward the absorption surface. The cavity can extend in a longitudinal direction of the probe, and the electromagnetic radiation source can be configured to emit electromagnetic radiation in the longitudinal direction of the probe.
According to one aspect of the invention, the probe is a friction stir welding pin, and the apparatus includes a rotatable actuator in rotational communication with the shank such that the rotatable actuator can rotate the shank about a longitudinal axis of the probe. According to another aspect, the probe is a friction stir welding blade, and the apparatus includes a reciprocatable actuator in reciprocatable communication with the shank.
The present invention also provides a method of friction welding at least one structural member. The method includes providing the at least one structural member, which can be formed of a material that plasticizes at a temperature of at least 800xc2x0 C. A friction welding probe is urged into the at least one structural member and actuated to frictionally weld the at least one structural member. An absorption surface of a shank in thermal communication with the probe is irradiated with electromagnetic radiation, such as light or radio frequency radiation, thereby heating the probe. For example, the light can be directed in a direction oblique relative to the absorption surface. The at least one structural member can be heated to a temperature of at least 800xc2x0 C.
According to one aspect of the invention, the probe is a friction stir welding pin, which is rotated about a longitudinal axis, and electromagnetic radiation is directed in the longitudinal direction of the pin and toward the pin. According to another aspect, the probe is a friction welding blade, which is reciprocated in an interface defined by the at least one structural member.